Chemists have long pondered the origins of the molecules necessary for life. Now possible clues have been found by Portuguese scientists, who have studied the interactions of naturally occurring salts with ribose, the sugar component of RNA. 

Ribose is widely distributed in life forms and participates in many biological processes, suggesting that it was around before life evolved. Given this, José da Silva and colleagues at the Technical University of Lisbon have looked into the sugar's beginnings in biological systems. 

The problem is, explains da Silva, that ribose occurs in modern biological structures exclusively as the less stable furanose isomer - how then did it come to be so common? The answer may lie in the presence of borate [B(OH)4-] in seawater, says da Silva, where life is thought to have originated. Borate binds just to the furanose isomer of ribose, making it more stable. His team has now found more evidence for borate's involvement in this process.

Borate may have stabilised ribose in the underwater environments suggested to be the birthplace of life

The researchers have shown that the ribose-borate complex is stable even under the conditions found around hydrothermal vents in the deep oceans. These have been suggested to be sites for the onset of life, but critics have emphasised ribose's instability in these environments, says da Silva. However, his group found that the ribose-borate complex was stable at temperatures up to 60 °C, as well as at alkaline pH, for extended periods of time. 'This,' he says, 'shows that, even under some adverse conditions, borate is still capable of interacting with ribose, inducing a predominance of the furanose isomer and increasing its stability.'

Antonio Lazcano, of the National Autonomous University of Mexico, Mexico City, who is president of The International Society for the Study of the Origin of Life, is positive about the group's findings. 'The results expand our understanding of the role of inorganic ions in stabilising compounds such as ribose under primitive environments where their accumulation and further processing could have taken place,' he says.

David Barden

This article has been updated (03 October 2008):  ribose is a component of RNA not DNA.